Many applications of the high T.sub.c oxide superconductors requires forming the superconductor into a wire. Current processes include forming a precursor of the oxide superconductor or the oxide superconductor itself into a wire and heat treating the wire to obtain an oxide superconductor wire. Current developments in high T.sub.c oxide superconductor processing have resulted in the manufacture of increasingly longer lengths of oxide superconductor wire with acceptable current carrying capacity.
The loading and unloading of oxide superconductor wire is an important step in the processing of the wire, in particular, to move the wire between wire deforming steps, such as pressing and rolling, and oxide superconductor phase-forming steps, such as sintering and annealing. The prior art wire deforming step is typically carried out by feeding the wire from a conventional spool through the deforming step and taking up the deformed wire onto a second conventional spool. Long lengths of wire can be efficiently wound onto the spool. However, the conventional spool is not readily adaptable for use in furnaces and results in inefficient use of furnace space. Further, the wire tends to sag and become distorted (wavy) because of the coiled form of the wire on the spool. Lastly, the multiple overlapping windings on the spool do not permit efficient oxidation and phase transformation of the oxide superconductor.
A further disadvantage to winding the oxide superconductor wire prior to heat treatment is that overlapping contact between portions of the wire results in diffusion bonding of the wire to itself and the mandrel, thereby degrading superconducting properties and preventing the unspooling of the heat treated wire. Silver is commonly used as a protective cladding for the oxide superconductor, in particular because the cladding itself is electrically conductive and does not prevent oxygen diffusion to the oxide superconductor. However, even the silver cladding will diffusion bond to other portions of the silver-cladded wire which are in contact during heat treatment.
U.S. Pat. No. 5,140,006 discloses a method and apparatus for coating a silver-cladded oxide superconductor wire with a diffusion-inhibiting material and taking up the coated wire onto a spool. Rare earth oxides are specifically disclosed as a desirable diffusion inhibiting material and no disclosure of the desirability of removing the material after treatment is disclosed.
It is the object of the present invention to efficiently process high-T.sub.c superconducting oxide wire by increasing the simplicity and efficiency of the method used to load and unload wire during processing, by reducing adhesion of the wire to itself and by maximizing the use of furnace space during heat treatment.